Wide latitude copy sheet

ABSTRACT

COPY SHEET MATERIAL, CONTAINING 10-80 PARTS BY WEIGHT OF SILVER SOAP AND CORRESPONDINGLY 90-20 PARTS BY WEIGHT OF FERRIC SOAP, EXHIBTS INCREASED EXPOSURE LATITUDE IN A HEAT-ACTIVATED COPYING PROCESS.

United States Patent once 3,795,532 Patented Mar. 5, 1974 U.S. Cl. 11736.2 7 Claims ABSTRACT OF THE DISCLOSURE Copy sheet material, containing 10-80 parts by weight of silver soap and correspondingly 90-20 parts by weight of ferric soap, exhibits increased exposure latitude in a heat-activated copying process.

This application is a continuation-in-part of our copending application Ser. No. 123,106, filed Mar. 10, 1971, now U.S. Pat. No. 3,682,684, issued Aug. 8, 1972.

BACKGROUND OF THE INVENTION This invention relates to sheet material useful in a heat-activated copying process, e.g., the thermographic copying process. In one important aspect the invention relates to heat-sensitive copy sheet in transparent film form with which projection transparencies of halftone originals may be prepared by thermographic copying processes.

The thermographic process as first described in Miller U.S. Pat. No. 2,740,896 involves brief exposure to intense radiation of an original in heat-conductive contact with a heat-sensitive copy sheet. In such processes the heat pattern produced at wide lines or blocky image areas may build up more rapidly than at narrow lines or areas of fine detail, resulting in blurring at the former or in partial copy at the latter areas when the copy sheet employed is deficient in exposure latitude. Copy sheet constructions based on a variety of silver soap reactants, as described in Owen U.S. Pat. No. 2,910,377, produce dense black images but the exposure must be carefully regulated in order to obtain a useful degree of latitude. Increased latitude is obtained with copy sheet constructions based on a variety of ferric soaps as described in Miller et al. U.S. Pat. No. 2,663,654, but even with these sheets it is found difficult to obtain fully satisfactory rendering of both fine and heavy lines or patterns.

SUMMARY OF THE INVENTION originals.

Accordingly, the present invention provides sheet material including a thin flexible backing having bonded thereto a thin coating comprising a mixture of 10-80 parts by weight of silver soap of long chain fatty acid and correspondingly 90-20 parts by weight of ferric soap of long chain fatty acid. Visible images are obtained on the sheet material upon localized heating thereof in the presence of suitable coreactant for the silver and ferric soaps. Thus, the novel sheet material is useful in the making of copies according to the thermographic copying process when it is associated with a source layer containing suitable coreactant for the silver and ferric soaps.

When using the novel sheet material to make copies of an original, the coreactant source layer is associated, in normally nonreactive relationship, with the soap layer to form a couplet; e.g., the coreactant may be provided as a separate coating directly overlying and bonded to the soap layer, or the coreactants may be provided as a coating on a separate sheet in a manner such that the coreactant can be transferred to the soap layer with heat during the thermographic copying process.

Thus, copies are easily made using the novel sheet material by (a) associating the soap layer of the sheet material with a source layer comprising thermally-transferable coreactant for the silver and ferric soaps to form a couplet, (b) positioning a differentially-radiation-absorptive original in contact with said couplet, and (0) exposing said original to intense radiant energy for a time suflicient to transfer coreactant to the soap layer and form a visible image on the sheet material.

Separate coreactants for the silver soap and ferric soap may be employed, but it has been found possible to use the same coreactant for both of the metal soap reactants. Polyhydric phenols such as pyrogallic acid, catechol, protocatechuic acid, azelayl pyrogallic acid, azelayl bispyrogallic acid, methyl gallate, butylyl pyrogallol, and behenoyl pyrogallol are particularly effective as coreactants for both the silver and ferric soaps. Mixtures of these and other coreactants for the metal soaps may also be used, e.g., to obtain images of preferred shades of color.

The silver and ferric soaps of long chain fatty acids (e.g., as described in Owen, U.S. Pat. 2,910,377, and Miller et al., U.S. Pat. 2,663,654, respectively) are suitable for use in the sheet materials of the present invention. The preferred soaps are silver behenate and ferric behenate. The silver and ferric soaps, along with polymeric film-forming binder, are typically mixed together and coated as a single layer on a suitable support.

Toners such as phthalazinone are known to improve the silver image in copy sheets based on silver soaps and are found desirable in the products of this invention, e.g., in amounts of about 10-20 percent of the weight of the metal soaps. Polymeric film-forming binders, nonfusing at the temperatures employed in copying, willordinarily be included in amounts sufiicient to form a smooth wellbonded coating. The compositions may be applied to paper or other nontransparent backings and when thus employed may contain pigments, fillers and other additives. Particularly desirable results are obtained using clear transparent coatings on transparent film backings, the resulting copies then serving admirably as projection transparencies for use on overhead projectors.

The following examples, in which all proportions are given in parts by weight unless otherwise indicated, will serve further to illustrate but not to limit the invention.

Example 1 A first coating composition is prepared by mixing together 20 parts of a 20% dispersion of ferric stearate in ethanol, 20 parts of a 20% dispersion of silver behenate in ethanol, 0.66 part of phthalazinone, 66.66 parts of a 15% solution of polyvinyl acetate in acetone, and 88.5 parts of acetone. The mixture is coated on two mil polyethylene terephthalate polyester film at a coating weight, after drying, of 0.55 gram per square feet.

A second coating composition, prepared by dissolving 20 parts of cellulose acetate butyrate and 4 parts of methyl gallate in parts of methylethyl ketone, is applied over the first coat at a coating weight, after drying, of 0.30

gram per square feet. The two coatings provide a thin visibly heat-sensitive sheet or couplet.

The coated film is clear and transparent, with a faint buff color. A portion of the couplet is placed in face-toface contact with an original having black printed characters on a white paper backing. Brief exposure of the original through the couplet to intense radiant energy in a thermographic copying machine results in the reproduction of the image areas on the sheet material. The image density is approximately 1.1. Images having a density above about 0.6 are effective in providing projection images which are easily visible when shown in a lighted room.

Another portion of the couplet is used to make a copy of a printed halftone original by a similar procedure. The dark image areas reproduce as a dense black; the reproductions of lighter areas are of much lower density and have a slightly purple cast.

Example 2 A silver soap dispersion is prepared by mixing together 60 parts of silver behenate, 240 parts of ethanol, 75 parts of polyvinyl acetate, 11.25 parts of phthalazinone, and

1089 parts of acetone.

A ferric soap dispersion is similarly prepared by mixing together 60 parts of ferric stearate, 240 parts of ethanol, 75 parts of polyvinyl acetate, and 1100 parts of acetone.

The two dispersions are mixed together in different pro portions as hereinafter tabulated. The mixtures are coated on one mil polyester film through a coating orifice of four mils, and the coatings are dried in an oven at temperatures not higher than about 200 F. Each sample is then further coated with a composition containing 9.8 parts of cellulose acetate butyrate and 2.0 parts of methyl gallate in 88.2 parts of methylethyl ketone, applied through a three mil orifice, and the sheet is again dried. The several samples or couplets are imaged thermographically by being placed against an original, printed with both Wide and narrow lines, which is then exposed through the sample to intense radiant energy for decreasing periods of time along the length of the lines. The test is conveniently carried out in a thermographic apparatus wherein the rate of movement of the copy sheet and printed original past a line source of intense radiation is uniformly increased, thereby providing a graphical representation of exposure latitude. Under unduly prolonged exposure the copy is blurred, the heavy lines in particular being broadened and showing rough wavy edges. With too short an exposure the density of the copy is decreased and the finest lines of the original do not reproduct. The range of exposures between these extremes represents the latitude of the copy sheet. The following tabulation provides a numerical indication of the relative latitude of copy sheets prepared and tested as above described and covering the range of 100% silver soap to 100% ferric soap in 10% increments.

TABLE L-EFFECT OF FerAg RATIO ON RELATIVE EXPOSURE LATITUDE Percent Agsoap 10 20 30 40 50 60 70 80 90 100 Pereent Fesoap 100 90 80 70 60 50 40 30 20 10 Latitude 33 37 40 46 47 52 50 51 50 18 11 Surprisingly, the latitude of the mixtures containing l0- 80% of silver soap is increased to a value far in excess of that obtained with either of the soaps alone.

Example 3 One mil polyester fihn is provided with a dried first coating of a mixture containing equal proportions of ferric stearate and silver behenate together with toner and binder, as described in connection with Example 1. Portions of the film are then separately coated with compositions containing two parts of difierent coreactants and 9.8 parts of cellulose acetate butyrate in 88.2 parts of methylethyl ketone, applied from a three mil coating orifice and again dried. The same coatings are applied over first coatings separately containing the two metal soaps, as controls. The several samples are tested for exposure latitude as previously described, with results as indicated in the following tubulation.

TABLE LIL-EFFECT OF COREAC'IANI ON RELATIVE EXPOSURE LATITUDE Example 4 Polyester film coated with mixed silver and ferric soaps as in Example 3 except for the inclusion in the coating composition of two parts of tetrachlorophthalic anhydride for each parts of metal soap and at a coating weight of 0.6 gram per square feet is further coated with a solution of 20 parts methyl gallate, 20 parts behenoyl pyrogallol, and 200 parts cellulose acetate butyrate in 18,000 parts of methylethyl ketone, applied at a coating weight after drying of 0.35 gram per square feet. The sheet is used in making a projection transparency of a screen process continuous tone print by the thermographic copying process. The image areas are of a more nearly uniform appearance than in the case of the film of Example 1, the image color being gray rather than purple at the lighter areas.

Example 5 A silver soap dispersion is prepared by mixing together 45 parts of silver behenate, 405 parts of methylethyl ketone, 67.5 parts of polyvinyl acetate, 6.75 parts of phthalazinone and 382.50 parts of acetone.

An iron soap dispersion is similarly prepared by mixing together 45 parts of iron tri-behenate, 405 parts of methylethyl ketone, 67.5 parts of polyvinyl acetate, 6.75 parts of phthalazinone and 382.50 parts of acetone.

The two dispersions are mixed together in different proportions as hereinafter tabulated. The mixtures are coated on two mil polyester film through a coating orifice of four mils and the coating dried in an oven at temperatures not higher than about 200 F. Part of each sample is then over-coated With a composition containing 10 parts cellulose acetate butyrate, 1.0 part methyl gallate, and 1.0 part butyryl pyrogallol in 35.2 parts of ethyl alcohol and 58.8 parts of acetone, applied through a two mil orifice, and the sheet is again dried. The several over-coated samples, or couplets, are imaged thermographically by being placed against an original, printed with both wide and narrow lines, which is then exposed through the sample or couplet to intense radiant energy for decreasing periods of time along the length of the lines. The test is conveniently carried out as described in Example 2. The following tabulation provides a numerical indication of the relative latitude of copy sheets prepared and tested as above described and covering the range of 100% silver soap to 100% iron soap in 10% increments.

TABLE IIL-EFEECT OF FezAg RATIO ON RELATIVE silver soap is surprisingly increased to a value far in excess of that obtained with either of the soaps alone.

Samples prepared and imaged according to the procedure of Example 5, except without the phthalazinone present, showed that the latitude 013 the mixtures containing -90% of silver soap were increased to a value in excess of that obtained with either of the soaps alone. The images obtained are brownish as compared to dense black images obtained when phthalazinone is present in the soap layer.

Example 6 followed by drying, a composition containing:

Parts Cellulose acetate butyrate 10 Methyl gallate 1.0 Butyryl pyrogallol 1.0 Ethyl alcohol 32.5 Acetone 58.8

Copies of a differentially-radiation-absorptive original are made by (a) positioning the coated face of the coreactant source layer against the soap layer of the sheet material to form a couplet, (b) positioning an original against the backing of the source layer, and (c) briefly exposing the original to intense radiant energy, through the soap layer and source layer of the couplet, in a thermographic copying machine, whereby a reproduction of the image areas of the original is formed on the sheet material due to the thermal transfer (in this case by volatilization) of coreactant from the source layer to the soap layer and the subsequent image-forming reaction of the soaps with coreactant.

Copies are also made as described above using a soap layer without the presence of phthalazinone.

Example 7 The silver soap dispersion and ferric soap dispersion of Example 5 are mixed together and coated onto two mil polyester film, through an orifice of four mils, followed by drying below 200 F., so as to provide a coating containing 50 parts of silver soap and 50 parts of ferric soap. The resulting sheet material is then overcoated with a compositioning containing 10 parts of cellulose acetate butyrate in 32 parts of ethyl alcohol and 58 parts of acetone, applied through a two mil orifice, followed by drying. The top coating acts as a transparentizing layer and as a protective layer for the soap layer.

The resulting sheet material is placed in face-to-face contact with the coreactant source layer described in Example 6 to form a couplet, placed against a differentiallyradiation-absorptive original, and exposed to intense radiant energy, through the couplet, in a thermographic copying machine to produce a copy of the original on the sheet material according to the procedure of Example 6.

What is claimed is:

1. Sheet material containing metal soap reactants and adapted for producing a copy of an original in a heatactivated copying process when associated with a coreactant source, said sheet material having a thin flexible backing and a thin coating bonded thereto which comprises a mixture of 10-80 parts by weight of silver soap of long chain fatty acid and correspondingly 90-20 parts by weight of ferric soap of long chain fatty acid.

2. Sheet material according to claim 1, wherein said soap layer contains 40-60 parts by weight of silver soap and correspondingly -40 parts by weight of ferric soap.

3. Sheet material according to claim 1, wherein said coating further contains a toner.

4. Sheet material according to claim 3, wherein said toner is phthalazinone.

5. Sheet material according to claim 1, wherein said silver soap is silver behenate and said ferric soap is ferric behenate.

6. A couplet adapted for use in the copying of a differentially-radiation-absorptive original in a heat-activated copying process, the couplet comprising:

(a) the sheet material of claim 1; and

(b) a source sheet comprising a backing having bonded thereto a thin coating comprising phenolic coreactant for said silver and ferric soap reactants; wherein said coreactant coating is in intimate contact with the soap layer of said sheet material.

7. Sheet material containing reactants adapted to produce a visible image when associated with a co-reactant source and heated in an imagewise manner, said sheet material comprising a thin flexible backing and having coated thereover 10-80 parts by weight of silver soap of long chain fatty acid and corresponding -20 parts by weight of ferric soap of long chain fatty acid.

References Cited UNITED STATES PATENTS 2,637,657 5/1953 Ozols 117-368 2,910,377 10/1959 Owen 117-369 2,999,035 9/1961 Sahler 117-36.8 3,107,174 10/1963 Wartman 117-368 3,168,864 2/1965 Brandl et a1. 117-368 3,185,585 5/1965 Baumann et a1 117-368 3,619,237 11/1971 Leclair 117-362 3,682,684 8/1972 Newman et al 1l7-36.9

MURRAY KATZ, Primary Examiner US. Cl. X.R.

117-369, 138.8 F, UA, 157; 106-26; 260-41 C UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent No. 3 795 53 Dated March 5, 197 1 Inventor(s) Donald J. Newman, Donald J. Williams & John R. Berg It is certified that error appears in the aboveddentifled patent and that said Letters Patent are hereby corrected as shown below:

Col 3, line 50, "reproduct" should read reproduce Col. 3, last column of figures in Table I should read Col. 5, line 17, "compositioning" should read composition T Col. 6, line 37, "corresponding" should read correspon- Signed and sealed this 8th day of April 1975.

(SEAL) Attest:

C. MARS-HALL DANN RUTH C. E'L-XSON Commissioner of Patents Arresting Officer and Trademarks 

